Device and method for optimising the circulation of a suspension in a plant comprising a three-phase reactor

ABSTRACT

A facility for chemical conversion of a feed comprises a reactor ( 2 ) containing a slurry constituted by at least one suspension of at least one solid in a liquid, a gas supply, a circuit that is external of the reactor, for continuous movement of a slurry stream, said slurry being withdrawn from at least one point (A) and at least a portion of which is re-introduced into at least one other point (B), a section for separating at least one fluid from the slurry traversing said external circuit, said facility further comprising:  
     means for stopping the circulation of said slurry in said circuit;  
     means for pressurised introduction of at least one fluid for draining the slurry contained in the circuit;  
     means for circulating the slurry in said external circuit under conditions such that the Reynolds number is more than 2500.

[0001] The present invention relates to an apparatus and a process forchemical conversion of a feed, for example hydrocarbons, in athree-phase reactor also known as a “slurry” reactor. The term “slurry”as used by the skilled person generally designates a suspension of solidparticles in a liquid, for example a suspension of fine particles with amean diameter that is generally about 200 micrometers or less, at aconcentration by weight of solid in the liquid that is usually in therange 0.1% to about 70%. The term “slurry” as used in the presentinvention also designates a mixture of a suspension as described above,also comprising a gas phase, i.e., a divided solid/liquid/gasthree-phase mixture. The reagents taking part in the chemical reactioncan be contained in the gas phase, in the liquid phase, in the solidphase or even in a plurality of those phases without transgressing thescope of the invention. Said solid phase can also be a reactioncatalyst.

[0002] Particular processes using a slurry reactor (three-phase) thatcan be cited are certain processes for converting and/or desulphurisingresidual heavy hydrocarbons or certain aliphatic oxidation or alkylationprocesses. Clearly, such processes do not limit either slurry reactionsor the field of application of the invention.

[0003] One of the major technical problems in slurry reactor processesis avoiding decantation of the solid or gradual clogging, which canresult in blockages in different parts of the facility. Moreparticularly, using a slurry process poses major problems connected withtransport of the slurry in the lines.

[0004] Curative means are already known that can limit the deposits orclean the lines by circulating a cleaning liquid.

[0005] Such means have been described, for example, in United Statespatents U.S. Pat. No. 4,526,764 and U.S. Pat. No. 4,123,601.

[0006] The Applicant has surprisingly discovered that circulation ofslurry under the particular conditions of the invention can avoid andprevent the onset of the clogging phenomenon in the slurry transportlines. A minimum slurry circulation velocity must be guaranteed to avoidsedimentation problems in the lines, which could lead to a blockage. Toolow a slurry circulation velocity causes the solid to be deposited inhorizontal or slightly inclined lines by sedimentation of the solid,leading to gradual obstruction thereof. When, for example, there are aplurality of circuits that are external to the reactor, it may bepossible to move from one circuit to another. In that case, some slurrylines are not longer traversed by slurry. The solid contained in thoselines sediments out, causing complete blockage of the circuit and toshutdown. Thus, it is impossible to re-use that circuit without firstcleaning and freeing it. In a further example, when a slurryrecirculation pump is shut down, the lines have to be rinsed with afluid to remove the solid deposited in those lines after the pump isstopped.

[0007] The present invention concerns an apparatus and an associatedprocess used in a facility employing a slurry reactor and with increasedreliability as regards the risk of deposition of solids and blockage ofdifferent parts of the facility compared with prior art devices. Theinvention advantageously avoids the onset of the phenomenon ofdeposition of solid particles contained in the slurry, for example inthe event of malfunction of the facility or when it is deliberately shutdown.

[0008] A further aim of the invention is to substantially reducemaintenance costs linked to deposition of solid in a slurry reactor.

[0009] To this end, the Applicant studied an experimental facility withdifferent programmes of slurry circulation in the reactor and in anexternal slurry circulation loop, used to carry out liquid/solidseparation and to recover the liquid produced by the chemical reaction.

[0010] Surprisingly, it was discovered that the risk of solid depositionis lower in the reactor than in the external loop. When the reactor isoperating normally, the suspension is kept stirred because of thesuperficial velocity of the gas V_(g) and sometimes by the use, inaddition to the gas effect, of a rising superficial liquid velocity. Theconditions for producing a stable suspension are known in the art. Suchconditions can avoid deposition of solid above the level at which thegas is injected into the reactor. By testing different conditions withthe onset of solid decantation, the Applicant found that during theonset of decantation, a substantially homogeneous suspension cangenerally be restored by increasing the superficial velocity of the gasby the simple expedient of injecting gas at a plurality of points.

[0011] In contrast, the Applicant discovered that the onset of soliddeposition in external circulation lines was difficult to eliminatesimply by increasing the slurry circulation rate. Thus, it is moredifficult to restore the optimal operating conditions, i.e., an absenceof deposition, for the external lines. Further, it has been discoveredthat the onset of deposition encourages subsequent deposition,aggravating the clogging process.

[0012] Further, the Applicant has surprisingly discovered that there isa correlation between the problems encountered and operationalperturbations, in particular during shutdown, however short.

[0013] Thus, the invention proposes a device that does not limit oreliminate deposition but mostly or completely prevents the onset of thedeposition process, which process accelerates once initiated.

[0014] Preferably, the invention also provides an apparatus withoptimised reliability that can avoid the initiation of the depositionprocess even in the event of non-availability of facility operators.This automated apparatus avoids the risk of mishandling, and limits thenumber of staff required to operate the facility properly.

[0015] To clean the lines of the external circuit effectively, inaccordance with the invention, the following steps must be carried out:

[0016] starting to rinse prior to deposition of a substantial fractionof the solid in the line, preferably prior to the onset of sedimentationof the solid in the line; if there are a plurality of lines in theexternal circuit, an automatic rinsing system is required;

[0017] providing a rinsing liquid rate that is at least higher than aminimum velocity to allow the solid particles in the horizontal orslightly inclined lines of the external circuit or circuits to move intosuspension; the volume of injected rinsing liquid is advantageously atleast twice the volume of the rinse line to ensure proper rinsingefficiency;

[0018] using a rinsing liquid that does not interact with the catalystto cause its deterioration and thus its deactivation;

[0019] preferably, using a rinsing liquid with a freezing point that isequal to or less than that of the liquid fraction of the slurry andgenerally less than ambient temperature to avoid said problems in theevent of shutdown of the facility.

[0020] In its most general form, the invention concerns a facility forchemically converting a feed, comprising at least one reactor containinga slurry constituted by at least one suspension of at least one solid ina liquid, a gas supply located in the lower portion of said reactor, acircuit that is external to the reactor, with continuous circulation ofa slurry stream, said slurry being withdrawn from at least one point (A)and at least a portion of which is re-introduced at at least one otherpoint (B) of said reactor, a section for separating at least one fluidcontained in the slurry stream traversing said external circuit, saidfacility being characterized in that it further comprises:

[0021] means for stopping the circulation of said slurry in saidcircuit;

[0022] means for pressurised introduction of at least one fluid fordraining the slurry contained in the circuit from at least one point (D)of said circuit;

[0023] means for circulating the slurry in said external circuit underconditions such that the Reynolds number is more than 2500 at everypoint in said circuit.

[0024] Preferably, said introduction point or points is/are placed insaid circuit between said means for stopping circulation of the slurryand said separation section.

[0025] In a first embodiment of the invention, at least one of saiddraining fluids is a pressurised gas.

[0026] In a further embodiment of the invention, which can be incombination with the previous embodiment, at least one of said drainingfluids is a pressurised liquid.

[0027] In general, said means for stopping circulation and draining saidslurry comprise:

[0028] at least one block valve disposed in said circuit;

[0029] means for bringing at least one introduction point (D) of thecircuit into communication with a source of at least one fluidpressurised to a pressure higher than that of point (D), said fluidbeing substantially free of solid in suspension;

[0030] a free volume in the upper portion of the reactor above theliquid/solid suspension, said volume being greater than the volume ofthe liquid/solid suspension contained in the circuit and in theseparation section.

[0031] Advantageously, said facility comprises means for detecting atleast one operational defect in said facility connected to means forcontrolling closure of the block valve and for opening at least onevalve placing said circuit into communication with said source ofpressurised fluid.

[0032] Typically, said reactor also comprises:

[0033] means for injecting said reactive gas at a plurality of points;

[0034] means for suspending and stirring the slurry in the reactor, of asize to avoid deposition of solid in the reactor above the gas injectionpoints.

[0035] In a preferred embodiment of the invention, said means forcirculating slurry in said external circuit are of a size so that saidReynolds number of the slurry is in the range 2500 to 500000 at everypoint in said external circuit.

[0036] Advantageously, said facility further comprises means forcondensing at least a portion of the gaseous effluent from said reactor(2), means (37) for storing at least a portion of the condensedeffluent, said storage means (37) being connected to means forintroducing the draining fluids into said circuit.

[0037] Most frequently, said solid in suspension is a reaction catalyst,and said pressurised fluid is a fluid that is chemically compatible withthe catalyst.

[0038] The present invention also concerns a process that can be carriedout by the facility in which a draining fluid is used at least partiallycomprising at least a fraction of at least one of the reaction fluids.

[0039] Still within the context of the invention, said draining fluidcan comprise, alternatively or in combination, at least one fluidselected from the group formed by nitrogen, hydrogen, carbon monoxide,liquid or vaporised hydrocarbons principally comprising compoundscontaining less than 20 carbon atoms, and mixtures formed completely orpartially from said different fluids.

[0040] In general, the freezing point of said draining fluid is lowerthan that of the liquid phase contained in the slurry and/or belowambient temperature.

[0041] The facility and/or process described above are applicable, forexample, to processes for conversion or desulphurisation of residualheavy hydrocarbons, to aliphatic alkylation processes, to oxidationprocesses.

[0042] The invention will be better understood from the followingdescription, illustrated in FIG. 1, showing a portion of a chemicalconversion facility incorporating a reactor and comprising a slurry asdefined above.

[0043]FIG. 1 shows a slurry reactor (2) comprising a line (1) in itslower portion for supplying a reactant gas, injected into a reactor (2)at a plurality of points (6). In the upper portion of the reactor (2) isa zone (5) for an essentially gaseous phase, located above the slurry.Said slurry is in a three-phase form and in the form of a continuousphase constituted by a liquid/solid suspension traversed by gas bubbles.

[0044] At the head of the reactor (2), a line (3) evacuates the gaseouseffluents from the reaction, comprising gases that have not beenconverted and gaseous reaction products. The gaseous effluents traversea cooling exchanger (4), with cooling causing condensation of a portionof the heaviest compounds that are separated in a separating drum (31).This drum can separate a gas phase evacuated via a line (32) from afirst liquid phase, for example water, evacuated via a line (33), andfrom a second liquid phase, for example the hydrocarbons produced by thereaction. Said hydrocarbons are then evacuated via a line (34). Thislast liquid phase is pumped using a means (35) then is reheated in aheat exchanger (36) under conditions that allow partial vaporisation ofsaid phase, which is subsequently fractionated in a separator drum (37).The gas phase arriving in drum (37) is evacuated via a line (38) onwhich a pressure regulating valve (39) is mounted, but it can also beevacuated via a line (46) comprising an automatically operated valve(41). The liquid phase, stored in the lower portion (40) of the drum(37), is evacuated via a line (47) which divides into two lines: a line(44) on which an automatically operated valve (43) is mounted and a line(45) on which an automatically operated valve (42) is mounted. Saidlines (44) and (45) are connected to a slurry circulating circuit,external to the reactor (2). Said circuit comprises a line (11) startingfrom a point (A) for withdrawing slurry from the reactor. Line (11)comprises an automatically operated block valve (14), and two points (C)and (D) for connecting respectively to lines (44) and (45), which arelines for circulating pressurised fluid originating from drum (37). Line(11) is connected to a separation zone (17). The gas contained in theslurry is separated in said zone (17) and evacuated via line (23) onwhich an automatically operated valve (24) is mounted. Zone (17) canalso advantageously separate a fraction of the liquid contained in theslurry, said fraction then being evacuated via a line (22). The residualslurry, free of substantially all of the gas and a portion of thecomponent liquid, is evacuated form zone (17) via a line (12), pumpedvia a means (16) such as a re-circulating pump, and sent to a line (13)on which an automatically operated valve (15) is mounted. Said residualslurry is then re-introduced into the reactor at a point (B) into a zonethat is preferably located in a lower portion of the reactor andupstream of point (A). In this case, the slurry is recycled to point (B)creates an upward movement of slurry in the reactor between points (B)and (A).

[0045] In the present description, the term “slurry stream” will be usedindiscriminately to describe the three-phase stream of slurry withdrawnfrom the reactor at point (A) or the stream of slurry that has beendegassed and concentrated by separating a portion of the liquid leavingzone (17) and circulating in lines (12) and (13). Separation zone (17)can in particular comprise means for gas/liquid or gas/liquid and solidseparation, for example a gas separator drum, and liquid/solidseparation means, for example a decanter, a hydrocyclone or a filter.The flow chart for zone (17), which is not a feature of the invention,will not be explained in detail. As is usual, said zone generallycomprises one or more spaces containing slurry, integrated into which isone or more of the means mentioned above.

[0046] The facility also preferably comprises automatic control meanssuch as a programmable controller (50) connected to the block valve (14)and to valves (41), 42) and (43). Advantageously, controller (50) canalso be connected to valve (15) and to valve (24) via means that are notshown, and to means with no reference numerals for detecting faults inthe operation of the facility.

[0047] The facility comprises at least one slurry type reactor (2)operating under pressure that can be varied depending on the chemicalreaction and/or the desired process, but typically in the range 1 to 5MPa (megapascals), for example about 2 MPa. Said reactor comprises adivided solid that can optionally but not necessarily be a catalyst. Thereactant gas mixture is introduced into line (1) and distributed in theslurry at a plurality of injection points (6). The number of injectionpoints is at least 2 points per square metre of horizontal block of thereactor, preferably in the range 4 to 400 points per square metre ofreactor, for example about 20 points per square metre.

[0048] In accordance with the invention, the reactor is stirredsufficiently to substantially prevent any deposition of solid above thegas injection points. In general, a superficial gas velocity V_(g) isused that is sufficient to obtain turbulent flow and not laminar flow,this velocity being readily determined in the laboratory.

[0049] For a slurry with an average granulometry of less than 100micrometers, for example, it is also possible to use a superficial gasvelocity V_(g) in the range 0.12 to 0.50 m/s, preferably in the range0.12 to 0.35 m/s, the upflowing superficial liquid velocity betweenpoints (B) and (A) of the reactor usually being greater than thedecantation rate of the solid, and generally in the range about 0.001 toabout 0.15 m/s, typically about 0.02 m/s. Said decantation rate iscalculated using standard rules, or it is measured in the laboratory.

[0050] Under these conditions, the slurry is sufficiently stirred toavoid substantial deposit of solid particles above the gas injectionpoints (6).

[0051] In one embodiment described with respect to FIG. 1, a stream ofslurry is circulated in the external circuit from point (A) to point (B)via lines (11), (12), (13), the quantity of slurry re-introduced intothe reactor at point (B) producing a superficial velocity of liquidV_(L) into the reactor.

[0052] The above conditions can also restore the correct suspension inthe reactor, after solid particles start to decant in the reactor, byincreasing velocities V_(G) and/or V_(L).

[0053] A portion of the liquid circulating in the external stream isseparated in a separation zone (17) comprising a filter or a decanter,to keep the slurry level in the reactor constant.

[0054] In accordance with the invention, pump (16) circulates the slurryin different lines of the circuit (11, 12, 13) with a sufficientvelocity in each line so that the Reynolds number, defined as

Re=ρVD/μ

[0055] in which:

[0056] ρ: density of slurry circulating in said line;

[0057] V: velocity of said slurry (calculated, for example, by assumingthat the gas velocity is identical to that of the suspension, in theparticular case of a three-phase slurry);

[0058] D_(H): hydraulic diameter of the line;

[0059] μ: viscosity of the slurry (typically, the single viscosity ofthe liquid/solid suspension, continuous phase);

[0060] is more than 2000, in particular more than 2500 and even 3000. Asan example, a Reynolds number can be selected that is in the range fromabout 3000 to about 500000, for example close to 20000. The rate ofcirculation of the slurry is preferably more than 0.30 n/s, for examplein the range 0.5 to 2 m/s. Preferably, the facility also comprises meansfor detecting at least one operational fault. This fault may beconnected with the reactor, for example too high a temperature, or anabnormal level of slurry in the reactor (2). In accordance with theinvention, said means can also monitor faults in the operation ofequipment external to the reactor, more particularly equipment in theseparation zone (17): gas/solid and liquid separator drum, decanter,filter, hydrocyclone, recirculation pump (16), etc . . .

[0061] In this case, in accordance with the invention, a series ofassociated means is provided for draining the external circuitimmediately, i.e., for evacuating the slurry contained in lines (11),(12) and (13) and in separation section (17), and for transferring thisslurry to the reactor. When the fault is detected, for example a faultin the operation of the separation section, the programmable controller(50) starts a procedure for draining the solution contained in theexternal circuit (11, 12, 13) before any substantial amount of slurryhas been deposited in the circuit, preferably before any solid particleshave sedimented out from the slurry. In accordance with the invention,this avoids long term clogging of the circuit, the solid then tending toadhere to the internal walls, facilitating subsequent clogging.

[0062] The preferred procedure for draining the circuit is an automatedprocedure controlled by the programmable controller (50). This procedurecomprises automatic closure of valves (14) and (24), said closurecausing recirculation of slurry in circuit (11, 12, 13) to stop and therelease of gas via line (23). The controller then automatically opens atleast one valve (41, (42) or (43), which places the circuit incommunication with a “clean” pressurised fluid, i.e., free of solid,said fluid displacing the slurry from the external circuit.

[0063] Preferably, the circuit is firstly placed in communication with asource of pressurised gas by opening the automatically operated valve(41) connected to the volume of gas contained in the upper portion ofthe drum (37). Alternatively, it is also possible to use, withoutdeparting from the scope of the invention, a further source of gas, forexample methane, reactor supply gas, or nitrogen. The pressure of thegas source employed is advantageously greater than at least 0.02 MPa atthe pressure for introducing gas into the circuit, i.e., at point. (D).Preferably, in accordance with the invention, a pressurised gas is usedthat is at a pressure that is greater than the pressure of the circuitby at least 0.1 MPa, preferably more than about 0.3 MPa.

[0064] The pressure differential between the gas source and the circuitis sufficient to force the slurry through the lines of the circuit witha local Reynolds number of more than 2500 at each point in the circuit(11, 12, 13) in the range 3000 to 500000 and preferably more than 2500.In accordance with the invention, the Reynolds number can neverthelessbe less than 2500, for example less than 2000 in the space or spacesincluded in the separation section (17), these advantageously havingwalls that are typically inclined by at least 60° to the horizontal.

[0065] Points (C) and (D) are preferably sufficiently close to valve(14) for at least 80%, preferably at least 90% and more preferably morethan 97% of the horizontal or slightly inclined portions of the circuit(11, 12, 13) to be flushed.

[0066] The circuit is generally drained rapidly, so it is possiblewithin the context of the invention to have a Reynolds number that islower than that used during normal operation of the facility; however,it is preferable to build in safety margins and use Reynolds numbersthat can vary along lines (11, 12, 13) but are in particular in therange 2500 to 500000, advantageously more than 10000, both during normaloperation and in the event of shutdown of the facility. In accordancewith the invention, closing the circuit using valve (14) and introducingpressurised gas between valve (14) and separation section (17) (whichincludes at least one space as defined above) via a line (45) candisplace the slurry contained in said space or spaces downstream of thecircuit and re-introduce it into the reactor at point (B). The durationof pressurised gas injection will be selected by the skilled person todisplace the major portion of the slurry contained in the circuit,including separation section (17). The terms “upstream” and “downstream”are defined in the present description with respect to the normal slurrycirculation direction, both in the reactor and in the external circuit.

[0067] After this gas injection, controller (5) then opens automaticallyoperated valve (42), to place the portion of the circuit downstream ofvalve (14) into communication with a clean liquid and at a pressure thatis higher than that present in said circuit, with a pressuredifferential that is, for example, similar to that previously describedfor the gas. This liquid will be displaced with a “piston” effect thatis greater than that of the residual slurry possibly remaining in thelines of said circuit. In accordance with the invention, it hassurprisingly been discovered by the Applicant that a liquid is moreeffective at draining slurry from the lines, while a gas is moreeffective for draining spaces such as those included in separationsection (17). A combination of a gas and a liquid introducedsimultaneously or preferentially one after the other (gas plus liquid)is thus preferred in the invention for carrying out said draining.

[0068] In a preferred embodiment of the invention, the block valve (14)located on the external slurry circuit of the reactor is used upstreamof a space included in a separation zone (17) and means for introducinga fluid under a pressure that is higher than that of said circuit, saidintroduction being carried out at a point located between said valve(14) and said space.

[0069] It is also possible, from commencing the draining procedure orafter closing valve (14), to open the automatically operated valve (43)to drain the upstream portion of the circuit. Preferably, pump (16) isstopped when the procedure is commenced.

[0070] In FIG. 1, the pressurised liquid contained in the lower portion(40) of drum (37) is obtained by condensing the gas from the reactorafter passage through exchanger (4). Said gas principally contains thelightest products produced in the reaction, in particular thosecontaining essentially less than 20 carbon atoms. The hydrocarbons arecondensed in drum (31) at a temperature of about 50° C., pumped by means(35), then re-heated and partially vaporised in exchanger (36) toproduce both a source of gas and a source of a liquid, at a pressurethat is higher than that of the slurry circulation circuit. To increasethe available gas flow, it is also possible to add nitrogen or methaneor a supply gas to reactor (2). These pressurised fluid sources are,clearly, chemically compatible with the catalyst. It is important-not touse fluids that can deactivate the catalyst.

[0071] In a preferred embodiment of the invention, in the processdescribed above, the major portion of the slurry contained in thecircuit is firstly purged by the pressurised gas, for example byintroducing via point (D) a volume of gas comprising, for example,between 1 and 5 times the volume of the liquid/solid suspensioncontained in the circuit, preferably between 1 and 3 times said volume.Then the residual slurry is purged by introducing via point (D) a volumeof pressurised liquid, for example in the range 0.5 to 3 times thevolume of the liquid/solid suspension initially contained in thecircuit, preferably between 0.5 and 1.5 times said volume. At the sametime as the circuit is purged via point (D), using the same pressurisedfluids (liquid and gas), the upstream portion of the circuit is purgedvia point (C), by circulating pressurised liquid in line (44). Theslurry contained in said portion of the circuit is then transferred tothe reactor at point (A).

[0072] When the circuit draining operations are completed, controller(50) initiates closure of the fluid supply valves (41), (42), (43) andclosure of valve (15) downstream of the circuit. The circuit can then beisolated, for example for maintenance, or re-activated by re-startingpump (16) and opening valves (14) and (15). Advantageously, theconnections for the slurry circuit to the reactor at points (A) and (B)are inclined, as shown in FIG. 1, so that no solid from the slurrycontained in the reactor can be deposited at the connections.

[0073] If the upstream portion of the circuit between point (A) andvalve (14) is inclined, for example by at least 60° to the horizontal,then this portion of the circuit does not need to be drained as solidparticles return to the reactor under gravity without adhering to theinclined walls.

[0074] In accordance with the invention, the reactor has a sufficientadditional free volume (5) at the reactor head above the slurry levelcorresponding to normal operation of the reactor to accept the surplusslurry from circuit (11, 12, 13) during draining thereof and also thevolume of pressurised liquid supplied to the circuit during draining.The free volume (gas) at the reactor head is larger than the volume ofthe liquid/solid slurry suspension initially contained in the circuit,including the separation section (17), during normal operation of thefacility.

[0075] This free volume can advantageously be in the range 1.1 to 20times the volume of the suspension in the circuit, preferably in therange 1.3 to 13 times this volume.

[0076] In accordance with the invention, it is not necessary for all ofthe operational faults of the facility to result in a shutdown ofcirculation and draining of the external slurry circuit. As an example,if slurry circulation pump (16) is duplicated and one of the two pumpsbreaks down, the other pump can be started by controller (50), thedefective pump can be purged with the pressurised liquid using theprocess described above, and that defective pump can be isolated byclosing the upstream and downstream valves, and the second pump willcirculate the slurry.

[0077] Immediate automatic shutdown of circulation and compete drainingof the slurry circuit are preferably reserved for major faults, inparticular with non duplicated equipment located in the circuit itself,which require the circuit to be shut down.

[0078] Thus, the invention proposes, in combination, an assembly oftechnical means that can prevent clogging and/or blockages in slurrytype reactor facilities, in particular to prevent problems in thedifficult case when an operational fault occurs in the slurrycirculation circuits. Thus, it can increase the reliability and reducemaintenance of facilities comprising a slurry reactor.

1. A facility for chemically converting a feed, comprising at least onereactor (2) containing a slurry constituted by at least one suspensionof at least one solid in a liquid, a gas supply located in the lowerportion of said reactor, a circuit (11, 12, 13) that is external to thereactor, with continuous circulation of a slurry stream, said slurrybeing withdrawn from at least one point (A) of the reactor and at leasta portion of which is re-introduced at at least one other point (B) ofsaid reactor, a section (17) for separating at least one fluid containedin the slurry stream traversing said external circuit (11, 12, 13), saidfacility being characterized in that it further comprises: means (14)for stopping circulation of said slurry in said circuit (11, 12, 13);means for pressurised introduction of at least one fluid for drainingthe slurry contained in the circuit from at least one point (D) of saidcircuit; means (16) for circulating the slurry in said external circuitunder conditions such that the Reynolds number is more than 2500 atevery point in said circuit (11, 12, 13).
 2. A facility according toclaim 1, in which said introduction point or points is/are placed insaid circuit (11, 12, 13) between said means (14) for stoppingcirculation of the slurry and said separation section (17).
 3. Afacility according to claim 1, in which at least one of said drainingfluids is a pressurised gas.
 4. A facility according to claim 1, inwhich at least one of said draining fluids is a pressurised liquid.
 5. Afacility according to claim 1, characterized in that said means forstopping circulation and draining said slurry comprise: at least oneblock valve (14) disposed in said circuit (11, 12, 13); means (41, 42,43, 44, 45, 46) for bringing at least one introduction point (D) of thecircuit into communication with a source of at least one fluidpressurised to a pressure higher than that of point (D), said fluidbeing substantially free of solid in suspension; a free volume (5) inthe upper portion of the reactor (2) above the liquid/solid suspension,said volume being greater than the volume of the liquid/solid suspensioncontained in the circuit and in the separation section (17).
 6. Afacility according to claim 5, characterized in that it comprises meansfor detecting at least one operational defect in said facility connectedto means (50) for controlling closure of the block valve (14) and foropening at least one valve (41, 42, 43) placing said circuit intocommunication with said source of pressurised fluid.
 7. A facilityaccording to claim 1, in which said reactor (2) further comprises: means(6) for injecting said reactive gas at a plurality of points; means forsuspending and agitating the slurry in the reactor, of a size to avoiddeposition of solid in the reactor (2) above the gas injection points.8. A facility according to claim 1, in which said means (16) forcirculating slurry in said external circuit are of a size so that saidReynolds number of the slurry is in the range 2500 to 500000 at everypoint in said external circuit.
 9. A facility according to claim 1,further comprising means for condensing at least a portion of thegaseous effluent from said reactor (2), means (37) for storing at leasta portion of the condensed effluent, said storage means (37) beingconnected to means for introducing the draining fluids into saidcircuit.
 10. A facility according to claim 1, in which said solid insuspension is a reaction catalyst, and said pressurised fluid is a fluidthat is chemically compatible with the catalyst.
 11. A process for usingthe facility according to claim 1, in which in which a draining fluid isused at least partially comprising at least a fraction of at least oneof the reaction fluids.
 12. A process for using the facility accordingto claim 1, in which the draining fluid is at least one fluid selectedfrom the group formed by nitrogen, hydrogen, carbon monoxide, liquid orvaporised hydrocarbons principally comprising compounds containing lessthan 20 carbon atoms, and mixtures formed completely or partially fromsaid different fluids.
 13. A process according to claim 11, in which thefreezing point of said draining fluid is lower than that of the liquidphase contained in the slurry.
 14. Application of a facility and/orprocess according to claim 1 to processes for conversion ordesulphurisation of residual heavy hydrocarbons, to aliphatic alkylationprocesses, or to oxidation processes.